At least 20 people were killed and five injured when gunmen opened fire in a bar late on Friday in the northern city of Monterrey, where the gang is fighting its former ally, the Gulf Cartel, said federal security spokesman Alejandro Poire.
Eleven bodies shot with high-powered rifles were found earlier on Friday, piled near a water well on the outskirts of Mexico City, where the gang is fighting the Knights Templar, Poire said. That is an offshoot of the La Familia gang that has terrorized its home state of Michoacan.
Poire said an additional 10 people were found dead early Saturday in various parts of the northern city of Torreon, where the Zetas are fighting the Sinaloa cartel headed by Joaquin "El Chapo" Guzman.
"The violence is a product of this criminal rivalry... surrounding the intent to control illegal activities in a community, and not the only the earnings that come with it, but also with transporting drugs to the United States," Poire said in a news conference.
Poire provided no more details on the killings in Torreon in the border state of Coahuila.
Coahuila state officials said the 10 bodies in Torreon had been mutilated and left in a sports-utility vehicle. Seven of the victims were men and three were women, and all had been killed several days earlier, said Fernando Olivas, a state prosecutor's representative in Torreon.
In Monterrey, 16 people died at the Sabino Gordo bar in the worst mass killing in memory in the northern industrial city, where violence has spiked since the Gulf and Zetas broke their alliance early last year. Four others died later at the hospital, said Jorge Domene, security spokesman for the state of Nuevo Leon, where Monterrey is located.
Domene said at a news conference that six people were wounded, two of them critically.
At least two men emerged from their vehicles and opened fire on the bar with AK-47s and AR-15s, Domene said. Several of the victims were employees of the bar, which has led police to conclude that employees were targeted, he said.
Cocaine was being sold at the bar and ziplock bags of drugs were found at the crime scene, Domene said.
Other downtown businesses closed earlier than usual after news of the massacre broke.
Outside Mexico City, police investigating the mass killing in the working class suburb of Valle de Chalco found one man alive along with 11 bodies and was taken to a hospital, said Antonio Ortega, a spokesman for the Mexico State police.
He said some of the bodies were blindfolded and had their hands tied. Poire said one woman was found seriously injured.
State officials said police found another body nearby a few hours later but could not confirm it was related to the mass attack.
The capital region has been largely spared the widespread drug violence that grips parts of Mexico.
But some poorer areas of the sprawling metropolis of 20 million people have begun to see killings and decapitations committed by street gangs that are remnants of splintered drug cartels.
In another incident allegedly involving the Zetas, the Mexican navy said Friday that it rescued a former mayor of Reynosa, across from McAllen, Texas, who had been kidnapped along with his son. Four alleged Zetas members were arrested at the scene after an anonymous tip that former Mayor Humberto Valdez was abducted Thursday, a navy statement said.
Also Saturday, the government announced it sent 1,800 federal police to the western state of Michoacan, where drug gang members have blocked highways and fired on officers in recent days. The force deployed with close to 200 vehicles, including ambulances, and also with Black Hawk helicopters.
Earlier in the week, federal police killed four gunmen who attacked them in Michoacan, triggering reprisal attacks by gang members who blocked highways with burning trailers, buses and pickup trucks.
Police said the gunmen were members of the Knights Templar, a criminal organization that split off from the La Familia cartel, a cult-like drug gang.
On Saturday, federal police killed three more riflemen after confronting them on a highway where they were trying to pull motorists out of their cars, the Michoacan state prosecutor's office said.
Poire repeated the government insistence that criminals, not the government's crackdown on organized crime, are causing the violence. More than 35,000 people have died since President Felipe Calderon stepped up the attack on organized crime in 2006, according to official figures. Some groups put the number at more than 40,000.
"The violence won't stop if we stop battling criminals," Poire said. "The violence will diminish as we accelerate our capacity to debilitate the gangs that produce it."
Federal authorities apprehended La Familia's alleged leader in late June, claiming the arrest was a debilitating blow to the gang. Jose de Jesus Mendez Vargas was alleged to be the last remaining head of the cartel, whose splinter group, the Knights Templar, continues to fight for control of areas La Familia once dominated.
Mexican authorities also arrested Jesus Enrique Rejon Aguilar, a co-founder of the Zetas drug cartel who is suspected of involvement in the February killing of a US customs agent.
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